A conventional cellular radio communication system achieves area coverage of a wide service area by dividing the wide service area into communication area units called cells, and allocating a base station to each communication area, the base station taking charge of radio communications with radio terminals within the communication area. As such a base station, used is a high-power base station (so-called a macrocell base station) having high transmission output power.
In recent years, attention have been paid to low-power base stations (so-called a picocell base station or a femtocell base station) having lower transmission output power than high-power base stations. When a low-power base station is installed in the cell of a high-power base station, the load of the high-power base station can be distributed to the low-power base station. Incidentally, a radio communication environment using a high-power base station and a low-power base station together is referred to as a heterogeneous deployment (see, for example, non-patent literature 1).